Exposure apparatus and exposure method

ABSTRACT

In a slit scan type projection exposure apparatus, a predetermined number of pulsed lights are emitted from a pulsed light source to transfer a pattern on a reticle to a wafer while the reticle and the wafer are scanned at a constant speed with respect to an exposure area on the wafer. At that time, not only fluctuations of the energies of the pulsed lights but also fluctuations of light emission timing of the pulsed lights are taken into consideration.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an exposure apparatus and anexposure control method and more particularly to a slit scan typeexposure apparatus equipped with an exposure control device forcontrolling an exposure amount and uniformity of luminous intensity to asensitive substrate within a predetermined range wherein a mask and thesensitive substrate are scanned synchronously to expose a pattern of themask on the photosensitive substrate an exposure method by use with theapparatus.

[0003] Also, the present invention relates to an exposure control devicefor controlling an exposure amount and uniformity of luminous intensityto a sensitive substrate within a predetermined range and an exposurecontrol method for the same.

[0004] 2. Related Background Art

[0005] In manufacturing semiconductors, liquid crystal display devicesor thin film magnetic heads, etc. under photolithography technique,projection exposure apparatuses have been utilized in which the patternof a photomask or a reticle (hereinafter called the reticle) is exposedvia a projection optical system on a photosensitive substrate such as awafer with photoresist applied thereto, a glass plate or the like.Recently, a chip pattern of a semiconductor, etc. tends to become largeand in the projection exposure apparatus, it is required to expose alarger portion of the pattern of a reticle on the photosensitivesubstrate.

[0006] Also, as the pattern of a semiconductor, etc. becomes minute,improvement of resolution of the projection optical system is required.In order to improve the resolution of the projection optical system, theexposure field of the projection optical system needs to be enlarged,which but is difficult in respect to the design or manufacture.Especially, when using a reflective and refractive system as theprojection optical system, there is a case that the shape of theexposure field with no aberration happens to be circular.

[0007] In order to deal with the problems of the tendency of enlargementof the pattern to be exposed and the limitation of the exposure field ofthe projection optical system, a method has been proposed in which areticle and a photosensitive substrate are scanned synchronously withrespect to, e.g., a rectangular, circular or hexagonal illumination area(hereinafter called the slit-shaped illumination area). That is, aso-called slit scan type projection exposure apparatus has beendeveloped in which the pattern of a reticle larger than a slit-shapedillumination area on the reticle is exposed on a photosensitivesubstrate, as disclosed in U.S. Pat. No. 4,822,975.

[0008] Generally, in the projection exposure apparatus, the condition ofa proper exposure amount and uniformity of luminous intensity withrespect to a photosensitive material of the photosensitive substrate isdetermined. Therefore, the slit scan type projection exposure apparatusis also provided with an exposure amount control device which makes anexposure amount to the photosensitive substrate coincide with a properexposure amount within a predetermined allowable range and maintains theuniformity of the luminous intensity of exposure lights to thephotosensitive substrate within a predetermined level.

[0009] Also, recently, it is required to enhance the resolution of thepattern to be exposed on the photosensitive substrate. A method forenhancing the resolution is to use shortwave exposure lights. Amongpresently usable light sources, an excimer laser light source, a pulseoscillation type laser source (pulsed light source) such as a metallicvaporization laser light source or the like emits shortwave exposurelights. However, the exposure energies (light amounts) of pulsed lightsemitted from the pulsed light source are fluctuated for the respectivepulses within a predetermined range.

[0010] Consequently, the exposure amount control device is controlledsuch that after the end of exposure, an integrated exposure amountbecomes a proper exposure amount within an allowable range. In theconventional exposure amount control device, when the average pulsedlight amount of pulsed lights from the pulsed light source is <p> andthe range of the fluctuations of the light amounts of the pulsed lightsis Δp, the parameter Δp/<p> representing the fluctuations of the lightamounts of the pulsed lights is deemed to become a normal distribution(actually random).

[0011] When the number N of pulsed lights emitted so as to be the properexposure amount (to a certain area (pulsed light integrated area) on thephotosensitive substrate which is scanned relatively with respect to anexposure area conjugate to the slit-shaped illumination area) is N, theexposure amount control device is controlled by using the fact that thefluctuations of the integrated exposure amount after the end of exposurebecomes (Δp/<p>)/N^(½).

[0012] When performing exposures by use with the pulsed light source inthe slit scan exposure method, how the light emission timing of thepulsed light source is set becomes a problem. For this matter,conventionally, when scanning the reticle and the photosensitivesubstrate synchronously, a light emission trigger signal is sent to thepulsed light source each time a stage on the side of the substrate ismoved for a predetermined distance. That is, a length measurement unit(e.g., laser interferometer) which measures the moving amount of thestage on the side of the substrate for scanning the substrate isutilized. And, light emission is performed in synchronism with theoutput of the length measurement unit.

[0013] In the above conventional technique, although the fluctuations ofthe light amounts of the pulsed lights emitted from the pulsed lightsource is taken into consideration, the fluctuations of the lightemission timing (the fluctuations of periods when the pulsed lightsource actually emits a pulsed light each time after a light emissiontrigger signal is sent to the pulsed light source) are not taken intoconsideration. However the inventors of the present invention found thatthe light emission timing of the pulsed light source affects the controlaccuracy of the exposure amount and the uniformity of luminousintensity.

[0014] Further, generally, in the length measurement unit (laserinterferometer or the like), there are fluctuations of the time whenafter performing actual measurement, it outputs the result of themeasurement. Therefore, in such a method for making the pulsed lightsource emit a pulsed light in synchronism with the output of the lengthmeasurement unit, the fluctuations of the timing of reading themeasurement result is added to the light emission timing of the pulsedlight source. Accordingly, it is not possible to maintain the controlaccuracy of the exposure amount and the uniformity of luminous intensitywithin the allowable range because of the influence of the fluctuationsof the timing reading the measurement results and the light emissiontiming of the pulsed light source.

SUMMARY OF THE INVENTION

[0015] In view of the above problems, it is an object of a presentinvention to provide an exposure apparatus capable of improving thecontrol accuracy of an exposure amount and the uniformity of luminousintensity to a photosensitive substrate when exposing a pattern of amask on the photosensitive substrate by use with a pulsed light sourcein a slit scan exposure method.

[0016] For achieving the above and other objects, an exposure apparatusfor transferring a pattern on a mask to a substrate comprises a lightsource for emitting pulsed lights; an illumination optical system forilluminating the mask with the pulsed lights; a mask stage supportingthe mask and being movable in a predetermined plane; a substrate stagesupporting the substrate and being movable in a plane parallel to thepredetermined plane; a drive section for moving the mask stage and thesubstrate stage synchronously; input means for inputting fluctuations ofenergies of a plurality of pulsed lights and fluctuations of the lightemission timing of the plurality of pulsed lights; first calculatingmeans for calculating the minimum number of pulses for a predeterminednumber of pulsed lights to be emitted to the substrate based on thefluctuations of the energies of the plurality of pulsed lights and thefluctuations of the light emission timing of the plurality of pulsedlights; second calculating means for calculating the moving speed of themask stage and the substrate stage based on the light emission timing ofthe plurality of pulsed lights and the minimum number of pulses; a drivecontrol section for controlling the drive section so as to move the maskstage and the substrate stage synchronously based on the calculatedmoving speed; and a control section for outputting a signal to saidlight source at regular intervals to emit said pulsed lights.

[0017] According to the above embodiment, not only the fluctuations ofthe energies of the pulsed lights but also the fluctuations of the lightemission timing are taken into consideration, the control accuracy ofthe exposure amount and the uniformity of the luminous intensity isimproved. Also, the light emission triggers are supplied to the pulsedlight source at regular intervals and the scan speed of the mask is thesame with that of the photosensitive substrate, so that the controlaccuracy of the exposure amount and the uniformity of the luminousintensity is further improved without being influenced by fluctuationsof the timing of reading the measurement result of a length measurementunit such as a laser interferometer.

[0018] It is an object of the present invention to provide an exposuremethod capable of improving control accuracy of an exposure amount anduniformity of luminous intensity to a photosensitive substrate whenexposing a pattern of a mask on the photosensitive substrate by a pulsedlight source in a slit scan exposure method.

[0019] For achieving the above and objects, in a second preferredembodiment, in a method of transferring a pattern on a mask to asubstrate by use with a light source for emitting pulsed lights, anillumination optical system for illuminating the mask with the pulsedlights, a mask stage supporting the mask and being movable in apredetermined plane, a substrate stage supporting the mask and beingmovable in a plane parallel to the predetermined plane and a drivensection for moving the mask stage and the substrate synchronously, thereare the step of inputting fluctuations of respective energies of aplurality of pulsed lights and fluctuations of light emission timing ofthe plurality of pulsed lights prior to exposing the substrate; the stepof calculating the minimum number of pulses for a predetermined numberof pulsed lights to be emitted to the substrate based on thefluctuations of the energies of the plurality of pulsed lights and thefluctuations of the light emission timing of the plurality of pulsedlights; the step of calculating a moving speed of the mask stage and thesubstrate stage based on the light emission timing and the minimumnumber of pulses; the step of moving the mask stage and the substratebased on the calculated moving speed; and the step of emitting thepredetermined number of pulsed lights at regular intervals at the timeof exposing the substrate.

[0020] Also, it is an object of the present invention to provide anexposure control device capable of improving the control accuracy of anexposure amount and the uniformity of the luminous intensity to aphotosensitive substrate.

[0021] For achieving the above and other objects, in a third preferredembodiment, in an exposure control device being provided in an exposureapparatus which has a pulsed light source for emitting pulsed lights inaccordance with respective light emission trigger signals from outsidethe pulsed light source, an illumination optical system for illuminatinga predetermined illumination area on a mask with the pulsed lights andscan means for scanning the mask and a substrate relatively with respectto the predetermined illumination area and exposes a pattern of the maskon the substrate while scanning the mask and the substrate relativelywith respect to the predetermined illumination area, the exposurecontrol device being for controlling an integrated exposure amount ofthe pulsed lights to the substrate and uniformity of luminous intensityon the substrate within predetermined accuracy, there is monitor meansfor measuring an energy of each of the pulsed lights to be emitted tothe substrate and light emission timing of the pulsed lights; a controlsection for emitting a plurality of pulsed lights from the pulsed lightsource prior to exposing the substrate; first calculating means forcalculating the average value of the energies of the plurality of pulsedlights and fluctuations of the light emission based on the measurementresult of the monitor means; second calculating means for calculatingthe minimum number of pulses for a predetermined number of pulsed lightsto be emitted to the substrate based on the fluctuations of the pulseenergies and the fluctuations of the light emission timing calculated bythe first calculating means, the minimum number being necessary forcontrolling the integrated exposure amount to the substrate and theuniformity of luminous intensity on the substrate within thepredetermined accuracy; light amount control means for controlling theenergies of the predetermined number of pulsed light to be emitted tothe substrate based on the minimum number of pulses for thepredetermined number of pulsed lights, a proper exposure amount and theaverage value of the plurality of pulse energies obtained by the firstcalculating means; and light emission control means for supplying thelight emission trigger signals at regular intervals to the pulsed lightsource so as to emit the respective pulsed lights.

[0022] Also, it is an object of the present invention to provide anexposure control method capable of improving the control accuracy of anexposing amount and the uniformity of the luminous intensity to aphotosensitive substrate.

[0023] For achieving the above and other objects, in a fourth preferredembodiment, in an exposure control method for controlling an integratedexposure amount of a predetermined number of pulsed lights emitted froma pulsed light source to a substrate and uniformity of luminousintensity on the substrate in predetermined accuracy, there are thefirst process of obtaining, by emitting a plurality of pulsed lightsfrom the pulsed light source prior to exposing the substrate, theaverage value of respective energies of the plurality of pulsed lights,fluctuations of the energies of the plurality of pulsed lights andfluctuations of light emission timing of the plurality of pulsed lights;

[0024] the second process of obtaining the minimum number of pulses forthe predetermined number of pulsed lights to be emitted to the substratebased on the fluctuations of the energies and the fluctuations of thelight emission timing obtained in the first process, the minimum numberbeing necessary for controlling said integrated exposure amount to thesubstrate and the uniformity of luminous intensity on the substratewithin the predetermined accuracy;

[0025] the third process of controlling the energies of thepredetermined number of pulsed lights to be emitted to the substratebased on the minimum number of pulses, a proper exposure amount to thesubstrate and the average value of the energies obtained in the firstprocess; and

[0026] a fourth process of sending a light emission trigger signal atregular intervals to the pulsed light source so as to emit the pulsedlights.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a schematic diagram showing the construction of a slitscan type projection exposure apparatus of an embodiment according tothe present invention;

[0028]FIG. 2 is a flowchart showing the exposure operation of theapparatus of FIG. 1;

[0029]FIG. 3A is a graph showing the distribution of the light amountsof pulsed lights;

[0030]FIG. 3B is a graph showing the distribution of the light emissiontiming;

[0031]FIG. 4 is a graph showing the luminous intensity distribution ofpulsed lights on the surface of a wafer; and

[0032]FIG. 5 is a timing chart showing light emission trigger pulsessupplied to a pulsed light source.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0033] An embodiment of the present invention will be described withreference to the accompanied drawings. In this embodiment, the presentinvention is applied to a slit scan type projection exposure apparatuswhich has a pulse oscillation type light source such as a laser lightsource.

[0034]FIG. 1 shows the projection exposure apparatus of the embodiment.A laser beam emitted from a pulse oscillation type pulsed light source 1enters a beam shaping optical system 2. The beam shaping optical system2 is constituted of cylindrical lenses or a beam expander and shapes thecross section of the laser beam such that the laser beam is incident ona fly eye lens 4 efficiently.

[0035] The laser beam emanated from the beam shaping optical system 2enters a light amount control means 3 which has a coarse control portionand a fine control portion for controlling the transmittance.

[0036] The laser beam emitted from the light amount control means 3 goesto the fly eye lens 4 which is provided for illuminating a field stop 7and a reticle R disposed in succession after the fly eye lens 4 withuniform luminous intensity.

[0037] The laser beam from the fly eye lens 4 enters a beam splitter 5with a small reflectance and a large transmittance.

[0038] The laser beam passed through the beam splitter 5 illuminates thefield stop 7 with uniform luminous intensity by means of a first relaylens 6. In this embodiment, the shape of the opening portion of thefield stop 7 is rectangular.

[0039] The laser beam passed through the field stop 7 is incident via asecond relay lens 8, a bending mirror 9 and a condenser lens 10 on thereticle R on a reticle stage 11. The laser beam from the field stop 7illuminates the reticle R with uniform luminous intensity.

[0040] The field stop 7, the pattern formed surface of the reticle R andthe exposure surface of a wafer W are conjugate. And, the laser beampassing through the reticle R enters a rectangular slit-shapedillumination area 24 which is conjugate with the opening portion of thefield stop 7 and disposed on the reticle R from under. It is possible toadjust the configuration of the slit-shaped illumination area 24 bychanging that of the opening portion of the field stop 7 by means of adrive section (not shown).

[0041] A portion of the pattern of the reticle R corresponding to theslit-shaped illumination area 24 is projected and exposed on a portionof the wafer W via a projection optical system 15. An exposure area 24Wof the wafer W is conjugate with the slit-shaped illumination area 24respect to the projection optical system 15.

[0042] Then, when the Z-coordinate is defined parallel to the opticalaxis of the projection optical system 15 and the scan direction of thereticle R with respect to the slit-like illumination area 24 (withrespect to the optical axis of the projection optical system 15) withina plane perpendicular to the optical axis is set to be the X direction,the reticle stage 11 is scanned by a reticle stage driving unit 12 inthe X direction.

[0043] The reticle stage driving unit 12 is controlled by a main controlsystem 13 for controlling the entire operation of the apparatus. Also,the reticle stage driving unit 12 is provided therein with a lengthmeasurement device (laser interferometer or the like) for detecting aX-coordinate in the X direction of the reticle stage 11. The lengthmeasurement device in the reticle stage drive unit 12 supplies themeasured X-coordinate to the main control system.

[0044] On the other hand, the wafer W is disposed via a wafer holder 16on a XY stage 17 which can be scanned at least in the X direction (thelateral directions in FIG. 1). Also, a Z stage (not shown) forpositioning the wafer W in the Z direction or the like is disposedbetween the XY stage 17 and the wafer holder 16.

[0045] In the slit scan exposure, when the reticle R is scanned in the+X direction (or −X direction), the wafer W is scanned synchronously inthe −X direction (or +X direction) with respect to the exposure area 24Wby means of the XY stage 17.

[0046] The main control system 13 controls the operation of the XY stage17 via a wafer stage driving unit 18. The wafer stage driving unit 18 isprovided therein with a length measurement device for detectingcoordinates in the X and Y directions of the XY stage 17. The lengthmeasurement device in the wafer stage drive unit 18 supplies themeasured X and Y-coordinates of the XY stage 17 to the main controlsystem 13.

[0047] The laser beam reflected from the beam splitter is received by anexposure light amount monitor 19 formed of a photoelectric converterdevice A photoelectric converting signal from the exposure light amountmonitor 19 is sent to a calculating unit 14 via an amplifier 20. Therelationship of the photoelectric converting signal and the luminousintensity of the pulsed light on the exposure surface of the wafer W isobtained in advance. That is, the photoelectric converting signal of themonitor 19 is calibrated in advance.

[0048] The calculating unit 14 measures fluctuations of the lightamounts of pulsed lights and the emission timing of the respectivepulsed lights by photoelectric converting signals from the monitor 19.The fluctuations of the light amounts of the pulsed lights as well asthe fluctuations of the emission timing of the pulsed lights aresupplied to the main control system 13. Also, at the time of eachexposure, the calculating unit 14 integrates the photoelectricconverting signal for each of pulsed lights to obtain the integratedexposure amount to the wafer W. The calculating unit 14 supplies theintegrated exposure amount to the main control system 13.

[0049] The main control system 13 supplies a light emission triggersignal TP to the pulsed light source 1 via a trigger controller 21 tocontrol the light emission timing of the pulsed light source 1.

[0050] Also, based on the timing of supplying light emission triggersignals TP via the trigger controller 21 to the pulsed light source 1and the light receiving timing detected by the calculating unit 14, thecalculating unit 14 calculates the fluctuations of the light emissiontiming (fluctuations of periods when the pulsed light source 1 emitsactually a pulsed light after each light emission trigger is supplied tothe pulsed light source 1) of the pulsed light source 1.

[0051] Further, the main control system 13 controls the output power ofthe pulsed light source 1 or the transmittance of the light amountcontrol means 3 as required. An operator can input various informationsuch as the information of the pattern of the reticle R, the width D(cm) of the slit-shaped exposure area 24W on the surface of the wafer Win the scan direction, the oscillation frequency f (Hz) of the pulsedlight source 1, etc. to the main control system 13 via an input/outputmeans 22. The main control system 13 is equipped with a memory 23 forstoring such various information (information of the pattern, etc.).

[0052] Next, an example of an operation for exposing the pattern of thereticle R on the wafer W with reference to the flowchart of FIG. 2.

[0053] First, in the step 101 of FIG. 1, the operator sets a desiredexposure amount S (mJ/cm²) on the surface of the wafer W to the maincontrol system 13 via the input/output means 22.

[0054] Next, in the step 102, the main control system 13 impartsinstructions for dummy light emission to the trigger controller 21.Then, with the wafer W retreated to the area where the wafer W will notbe exposed (area outside the exposure area 24W), the experimental lightemission (dummy light emission) of the pulsed light source 1 isperformed. In the dummy light emission, pulsed light for, e.g., about100 pulses are emitted. The distribution of the pulsed light amounts andthe distribution of the light emission timing become approximatelynormal distributions as shown in FIG. 3. The distributions of the pulsedlight amounts and the light emission timing are known from thephotoelectric converting signals from the exposure light amount monitor19.

[0055]FIG. 3A shows the distribution of the values (mJ/cm²) of the lightamounts P (reduced values to the exposure surface of the wafer W) of therespective pulsed lights measured in the dummy light emission. Also,FIG. 3B shows the distribution of the light emission timing δ (sec) ofthe pulsed light source 1 measured in the dummy light emission.

[0056] In the step 103, the calculating unit 14 obtains the averagepulsed light amount <p>(mJ/cm²) on the exposure surface of the wafer Wfrom the distribution data of the pulsed light amounts P shown in FIG.3A and the average value <δ> of the fluctuations of the light emissiontiming from the distribution data of the light emission timing δ shownin FIG. 3B.

[0057] Thereafter, in the step 104, the calculating unit 14 obtains thedeviations Δp of the pulsed light amounts at three times the standarddeviation (3σ) from the distribution data of the pulsed light amounts pof FIG. 3A. Also, the calculating unit 14 obtains the deviations Δδ ofthe light emission timing at three times the standard deviation from thedistribution data of the light emission timing δ of FIG. 3B. Then, thecalculating unit 14 calculates the fluctuations (Δp/<p>) of the pulsedlight amounts and the fluctuations (Δδ/<δ>) of the light emissiontiming.

[0058] Next, in the step 105, the desired exposure amount S (mJ/cm²)specified via the input/output means 22 is sent from the main controlsystem 13 to the calculating unit 14, which then calculates the number Nof exposure pulses by use with the desired exposure amount S and theaverage pulsed light amount <p> calculated in the step 103 from thefollowing equation:

N=int(S/<p>),  (1)

[0059] wherein int (A) represents the integer obtained by discarding thedecimal fraction of the real number A.

[0060] Also, the main control system 13 sends the information such asthe width D (cm) of the slit-shaped exposure area 24W on the wafer W inthe scan direction and the oscillation frequency f (Hz) of the pulsedlight source 1 from the memory 23. to the calculating unit 14 Thecalculating unit 14 obtains the scan speed v (cm/sec) on the surface ofthe wafer by use with the number N of exposure pulses, the width D andthe frequency f from the following equation: $\begin{matrix}{v = \frac{D \cdot f}{N}} & (2)\end{matrix}$

[0061] Thereafter, in the step 106, the calculating unit 14 calculatesthe minimum number Nmin of exposure pulses. The minimum number Nmin ofexposure pulses is necessary for controlling the integrated exposureamount on the exposure surface of the wafer W and the uniformity of theluminous intensity within predetermined accuracy. The equation forcalculating the minimum number Nmin of exposure pulses will be describedin detail later. The number N of exposure pulses and the minimum numberNmin of exposure pulses are supplied to the main control system 13.

[0062] Next, in the step 107, the main control system 13 compares thenumber N of exposure pulses with the minimum number Nmin of exposurepulses. When N<Nmin holds as the result of the comparison, the maincontrol system 13 lowers the transmittance of the light amount controlmeans 3 (coarse adjustment) as in the step 108. Thereafter, the steps102 to 107 are repeated and the number N of exposure pulses is againcompared with the minimum number Nmin of exposure pulses. Accordingly,the transmittance of the light amount control means 3 is set such thatN≧Nmin holds finally. As an example of means for performing the coarseadjustment of the transmittance, there is a device formed by mounting aplurality of ND filters with different transmittances to a turret plate,as disclosed in Japanese Patent Laid-Open Application No. 63-316430 andU.S. Pat. No. 4,970,546.

[0063] Next, when N≧Nmin in the step 107, the fine adjustment of pulsedlight amounts is performed. That is, the average pulsed light amount <p>is finely adjusted such that S/<p> in the equation (1) becomes asinteger. At this time, as the scan speed v has been determined inaccordance with the number N of exposure pulses obtained from theequation (1) in the step 105, it is preferable to adjust the pulsedlight amounts finely so as not to change the number N of exposurepulses, i.e., so as to make the average pulsed light amount <p> slightlylarger. On the other hand, if the average pulsed light amount <p>becomes slightly smaller by the fine adjustment of the pulsed lightamounts so that the number N of exposure pulses becomes N+1, the scanspeed v should be calculated again by the equation (2).

[0064] As an example of the fine adjusting means for adjusting pulsedlight energies finely, there is means with two gratings which isdisposed along the optical light path of pulsed lights and formed withrespective line and space patterns arranged at the same pitch and amechanism for moving the two gratings slightly laterally with respect toeach other, as disclosed in the Japanese Patent Application Laid-openNo. 2-135723. When utilizing these two gratings, pulsed lights in areaswhere bright portions of the first grating overlap with those of thesecond grating are directed to the wafer. Therefore, it is possible toregulate the amounts of pulsed lights directed toward the wafer W finelyby controlling the relative lateral moving amount of the two gratings.

[0065] Then, in the step 110, the main control system 13 starts scanningthe reticle R and the wafer W via the reticle stage 11 and the XY stage17 under the wafer W respectively. In FIG. 1, e.g., when the reticle Ris scanned in the X direction, the wafer W is scanned in the −Xdirection. Also, although the scan speed V (reduced value on theexposure surface of the wafer W) of the reticler R and the wafer W isdetermined by the equation (2) in this embodiment, the time for makingthe scan speed of the XY stage 17 under the wafer W reach the scan speedv after the start of scanning is set to be T₀.

[0066] Further, after resetting the time t and the parameter j to zeroat the time of the start of scanning, and when the time t becomes(T₀+jΔT), the main control system 13 supplies a light emission triggersignal TP (a pulse of the high level “1”) via the trigger controller 21to the pulsed light source 1. Accordingly, the pulsed light source 1emits a pulsed light to expose a portion of the pattern of the reticle Ron a portion of the wafer W.

[0067]FIG. 5 shows the light emission trigger signal TP. From the momentwhen the time t reaches T₀, the light emission trigger signal TP isemitted in constant cycles ΔT. Thereby, the pulsed light source 1 emitsa pulsed light in each cycle ΔT and the oscillation frequency f isexpressed by 1/ΔT. The oscillation frequency f is the value stored inthe memory 23 in advance. Then, in the step 112, 1 is added to theparameter j. When the parameter j has not reached the integer N_(T), thepulsed light source 1 emits a pulsed light on the constant frequency (inthe constant cycles ΔT) until the light emissions of N_(t) pulses areperformed.

[0068] When the width of a shot area on the wafer n the scan direction(X direction) is L1 and the width of the exposure area 24W in the scandirection is D, the minimum number N_(T) of pulsed lights is as followssince the distance by which the wafer W is scanned per a cycle of thelight emission of the pulsed light source 1 is v/f.

N _(T)=(L1+D)/(v/f)

=(L1+D)f/v.

[0069] Actually, at the start and end of scanning, a predeterminednumber of pulsed lights are added. Then, in the step 113, when thenumber of emitted pulsed lights has reached N_(t), the main controlsystem 13 finishes the scanning and exposure of the reticle R and thewafer W in the step 114. Consequently, the whole pattern of the reticleR is transferred to a shot area of the wafer W. In this case, the lightemission of the pulsed light source 1 is performed on the constantfrequency regardless of the X-coordinate of the reticle stage 11 and theX-coordinate of the XY stage 17 on the side of the wafer W in thisembodiment. However, the main control system 13 scans the reticle stage11 and the XY stage at respectively constant speeds via the reticlestage driving unit 12 and the wafer stage driving unit 18. Therefore, inthis embodiment, even though the time for measuring the X-coordinate ofthe reticle stage 11 or the time for measuring the X-coordinate of theXY stage 17 on the side of the wafer W is varied, the oscillationfrequency of the pulsed light source 1 will not be influenced by thatmatter and the integrated exposure amount with respect to the wafer Wand the uniformity of the luminous intensity are maintained in thedesired accuracy.

[0070] Next, the method of calculating the minimum number Nmin ofexposure pulses in the step 106 of FIG. 2 will be described. First,although the illumination field (illumination area 24) and the exposurearea 24W on the wafer W are formed by the field stop 7 in FIG. 1, theshapes of the luminous intensity distributions along the cross sectionsof the illumination area 24 and the exposure area 24W in the scandirection are ideally rectangular. However, actually, the shapes thereofbecome like trapezoids as shown in FIG. 4 owing to the positioning errorof the field stop 7, aberrations of the optical system, etc.

[0071]FIG. 4 shows luminous intensity distributions of respective pulsedlights with respect to the X position on the wafer W in the scandirection by the function p of the position X. For example, if lightemitted from a point in the opening portion of the field stop 7 isblurred on a circular area with the radius ΔD on the wafer W withuniform luminous intensity, the slope portions of the trapezoid likeluminous intensity distribution are proved easily to be the followingfunction of a variable (X/ΔD): $\begin{matrix}{{{p\left( {{X/\Delta}\quad D} \right)} = {\frac{1}{\pi}\left\{ {{\arccos \quad \left( \frac{X}{\Delta \quad D} \right)} - {\left( \frac{X}{\Delta \quad D} \right)\sqrt{1 - \left( \frac{X}{\Delta \quad D} \right)^{2}}}} \right\}}}\left( {{- 1} \leqq \frac{X}{\Delta \quad D} \leqq {+ 1}} \right)} & (3)\end{matrix}$

[0072]FIG. 4 shows the luminous intensity distributions along the crosssections with blurred portions by the distribution curves 25A, 25B and25C for the respective pulsed lights. The actual width of the exposurearea 24W in the scan direction is about a few mm and the width ΔD of theblurred portions is about 10 μm or more, so the luminous intensitydistributions along the cross sections of FIG. 4 are approximatelyrectangular. The peak values of the distribution curves 25A, 25B and 25Care p1, p2 and p3 and the width of the distribution curves 25A, 25B and25C in the scan direction at positions where the values p1, p2 and p3become half is D commonly. Then, the width D can be deemed to be thewidth of the exposure area 24W in the scan direction.

[0073] Further, in FIG. 4, the peak values p1, p2 and p3 respectivelyfor the first pulse (distribution curve 25A), the second pulse(distribution curve 25B) and the third pulse (distribution curve 25C)are varied due to the fluctuations of the pulsed light amounts and theintervals of the emissions of the pulsed lights are not also constantdue to the fluctuations of the light emission timing. Here, in the slopeportions on the lateral sides of the distribution curve 25A for thefirst pulse, when the number of pulses for overlapped exposures on andafter the second pulse with respect to areas (with the widths ΔD₁ andΔD₂) where the light amount values are half the peak value or less is N₁or N₂, the following equations hold: $\begin{matrix}{{N_{1} = {{int}\quad \left( {\frac{\Delta \quad D_{1}}{D} \cdot N} \right)}},{N_{2} = {{int}\quad {\left( {\frac{\Delta \quad D_{2}}{D} \cdot N} \right).}}}} & (4)\end{matrix}$

[0074] That is, as the number of pulses for exposures during thescanning of the exposure area with the width D is N (equation (1)),pulsed lights the number of which is proportional to each of the widthsΔD₁ and ΔD₂ are emitted to the respective areas with the respectivewidths ΔD₁ and ΔD₂. At this time, the accuracy A of the exposure amountafter the scan exposure and the uniformity of the luminous intensity isexpressed by the following equation. For example, when the accuracy is1%, A is 0.01. $\begin{matrix}\begin{matrix}{A = \quad {+ \left\{ {1 - \frac{N_{1} + N_{2} + 1}{2N} + {\left( \frac{D}{2{N \cdot \Delta}\quad D_{1}} \right)2\quad \frac{N_{1\quad}}{3N}\left( {N_{1} + 1} \right)\left( {{2N_{1\quad}} + 1} \right)} +} \right.}} \\{{\left. \quad {\left( \frac{D}{2{N \cdot \Delta}\quad D_{2}} \right)2\quad \frac{N_{2\quad}}{3N}\left( {N_{2} + 1} \right)\quad \left( {{2N_{2}} + 1} \right)} \right\}^{\frac{1}{2}} \times \frac{1}{\sqrt{N}}\left( \frac{\Delta \quad p}{\langle p\rangle} \right)} +} \\{\quad {{\left\{ {\frac{{2N_{1}} + 1}{\left( {2\Delta \quad D_{1}} \right)^{2}} + \frac{{2N_{2}} + 1}{\left( {2\Delta \quad D_{2}} \right)^{2}}} \right\}^{\frac{1}{2}}\left\{ {\left( \frac{\Delta \quad p}{\langle p\rangle} \right)^{2} + \left( \frac{\Delta \quad \delta}{\langle\delta\rangle} \right)^{2}} \right\}^{\frac{1}{2}}\frac{X}{N}} +}} \\{\quad {{{{\frac{{2N_{2}} + 1}{2\Delta \quad D_{2}} - \frac{{2N_{1}} + 1}{2\Delta \quad D_{1}}}}\frac{X}{N}},\left( {{- \frac{D}{N}} \leqq X \leqq {+ \frac{D}{N}}} \right)}}\end{matrix} & (5)\end{matrix}$

[0075] In the right side of the equation, the first member is producedby the fluctuations of the light amounts of pulsed lights, the secondmember is produced by the fluctuations of the light amounts of thepulsed lights and the fluctuations of the light emission timing and thethird member expresses the deterioration of the uniformity of luminousintensity caused by the dissymmetry of the blurred portions in theexposure area 24W. The widths D, ΔD₁ and ΔD₂ are stored in the memory 23as the constants of the apparatus in this embodiment. However, thefunction of measuring the widths D, ΔD₁ and ΔD₂ may be provided in theexposure apparatus. Also, (Δp/<p>) and (Δδ/<δ>) are obtained by theactual measurement as in the step 104. Accordingly, the minimum numberNmin can be obtained by substituting the desired accuracy A in theequation (5) and solving N.

[0076] In the above embodiment, the description of control means forreducing the interference pattern produced by the spatial coherency ofthe pulsed light source 1 and unevenness of illumination (speckle) isomitted. Generally, the excimer laser has preferable spatial coherency,so that the exposure apparatus using the excimer laser light source isequipped with interference pattern reducing means and exposure controlis performed while reducing the interference pattern by exposures for aplurality of pulses (e.g., U.S. Pat. No. 4,970,546). In this case, thelarger number between the minimum number of exposure pulses necessaryfor reducing the interference pattern and the minimum number Nmin ofexposure pulses obtained from the equations (4) and (5) should bedetermined as Nmin.

[0077] Although the exposure amount monitor 19 is provided in theillumination optical system, the monitor 19 may be substituted for asensor provided on the wafer stage (16, 17). However, such a sensorprovided on the wafer stage can be used only in the dummy light emissionof the pulsed light source 1. Then, another exposure amount monitor isrequired when actual exposures are performed to the wafer W.

[0078] Also, the slit-shaped illumination area is in the shape of arectangular in this embodiment, but may be in the shape of a hexagon,rhomb or a circle. Further, the projection optical system 15 may be arefractive type, a reflective type or a refractive and reflective type.And, the pulsed light source 1 may be a plasma X-ray light source, asynchrotron radiation apparatus (SOR) other than the laser light source.Furthermore, needless to say, the present invention are effective notonly in the projection exposure apparatus but also in a contact type ora proximity type exposure apparatus.

[0079] It will be understood that various structural changes andmodifications may be made without departing from the scope of theinvention set forth in the accompanying claims.

1. A scanning exposure method comprising: performing an intensityadjustment so as to determine intensity of an exposure beam; after theintensity adjustment, beginning to move a mask and a substrate insynchronism with each other; and starting to emit pulses of the exposurebeam after the beginning of the synchronous movement.
 2. A methodaccording to claim 1 , wherein the pulses are emitted at a constantinterval.
 3. A method according to claim 1 , wherein the emission of thepulses starts after the lapse of a predetermined time from the beginningof the synchronous movement until a moving speed of the substratereaches a predetermined scanning speed.
 4. A method according to claim 3, wherein the predetermined scanning speed is determined based on anoscillation frequency of the pulses.
 5. A method according to claim 3 ,wherein the predetermined scanning speed is determined based on a widthof said exposure beam in a moving direction of the substrate.
 6. Amethod according to claim 1 , wherein the emission of the pulses startsbased on a time required for a moving speed of the substrate to become apredetermined scanning speed.
 7. A method according to claim 1 , furthercomprising: controlling emission timing of the pulses so as to maintainan integrated exposure amount for the substrate in a desired accuracy.8. A method according to claim 1 , wherein a first pulse of the pulsesis emitted after the elapse of a variable period.
 9. A method accordingto claim 8 , wherein the variable period is determined based on a timerequired for a moving speed of the substrate to become a predeterminedscanning speed.
 10. A method according to claim 1 , wherein a scanningexposure of a shot area on the substrate is performed so as to satisfythe following condition: v=D·f/N wherein, v: a scanning speed of thesubstrate during the scanning exposure; D: a width in a moving directionof the substrate, of the exposure beam incident on the substrate duringthe scanning exposure; f: an oscillation frequency of pulses of theexposure beam during the scanning exposure; N: the number of pulses ofthe exposure beam with which each point on said substrate is irradiatedduring the scanning exposure.
 11. A method according to claim 10 ,wherein the scanning speed v is determined based on the oscillationfrequency f, the width D, and a proper exposure dose of the substrate.12. A method according to claim 1 , further comprising: before theintensity adjustment, performing a dummy emission in which pulses of theexposure beam are emitted in order to measure the intensity of theexposure beam.
 13. A method for manufacturing a microdevice including anexposure process in which a shot area on a substrate is exposed to forma device pattern on the shot area by moving the substrate and a maskpattern relative to an exposure beam, the method comprising: performingan intensity adjustment so as to determine intensity of the exposurebeam; after the intensity adjustment, beginning to move the mask patternand the substrate in synchronism with each other; and starting to emitpulses of the exposure beam after the beginning of the synchronousmovement.
 14. A scanning exposure apparatus comprising: a scanningsystem including a mask stage for holding a mask, a substrate stage forholding a substrate, a first driving system for moving the mask stage,and a second driving system for moving the substrate stage, which movesthe mask and the substrate synchronously to expose the substrate; anillumination system including a beam source and an optical member usedfor adjusting intensity of an exposure beam from the beam source, whichdirects the exposure beam to the mask, wherein an intensity adjustmentis performed by using the optical member before the scanning systembegins to move the mask and the substrate synchronously; and an emissioncontrol system including a trigger system that is connected to the beamsource and supplies a trigger signal to the beam source, which controlsemission timing of the beam source, wherein the beam source starts toemit pulses of the exposure beam after the scanning system begins tomove the mask and the substrate synchronously.
 15. An apparatusaccording to claim 14 , wherein the beam source starts to emit thepulses after the lapse of a predetermined time from the beginning of thesynchronous movement until a moving speed of the substrate reaches apredetermined scanning speed.
 16. An apparatus according to claim 14 ,wherein the beam source starts to emit the pulses based on a timerequired for a moving speed of the substrate to become a predeterminedscanning speed.
 17. An apparatus according to claim 14 , wherein ascanning exposure of a shot area on the substrate is performed so as tosatisfy the following condition: v=D·f/N wherein, v: a scanning speed ofthe substrate during the scanning exposure; D: a width in a movingdirection of the substrate, of the exposure beam incident on thesubstrate during the scanning exposure; f: an oscillation frequency ofpulses of the exposure beam during the scanning exposure; N: the numberof pulses of the exposure beam with which each point on said substrateis irradiated during the scanning exposure.
 18. A method for making ascanning exposure apparatus comprising: providing a scanning systemincluding a mask stage for holding a mask, a substrate stage for holdinga substrate, a first driving system for moving the mask stage, and asecond driving system for moving the substrate stage, which moves themask and the substrate synchronously to expose the substrate; providingan illumination system including a beam source and an optical memberused for adjusting intensity of an exposure beam from the beam source,which directs the exposure beam to the mask, wherein an intensityadjustment is performed by using the optical member before the scanningsystem begins to move the mask and the substrate synchronously; andproviding an emission control system including a trigger system that isconnected to the beam source and supplies a trigger signal to the beamsource, which controls emission timing of the beam source, wherein thebeam source starts to emit pulses of the exposure beam after thescanning system begins to move the mask and the substrate synchronously.19. A scanning exposure apparatus comprising: means for performing anintensity adjustment so as to determine intensity of an exposure beam;means for moving a mask and a substrate synchronously for scanningexposure, wherein the synchronous movement begins after the intensityadjustment; and means for controlling emission of pulses of the exposurebeam, wherein the emission of the pulses starts after the beginning ofthe synchronous movement.